Iodine cycle incandescent electric lamp



March 15, 1966 J. F. ENGLISH ETAL 3,240,975

IODINE CYCLE INCANDESCENT ELECTRIC LAMP Filed Feb. 20, 1963 3 h l wmssrsm FILAMENT 1 1 IODINE AND ARGON, KRYPTON i: 1 OR XENON II 7 2: 8y) If] Irwvezn tors:

James F Enghish Edward G. Zubtev Their A -t ovneg United States Patent M 3,240,975 ISDINE CYCLE iNCANDESCENT ELECTRIC LAMP James F. Engiish, Lakewood, and Edward G. Zubier,

Chagrin Falls, Ohio, assignors to General Electric Company, a corporation of New York Filed Feb. 20, 1963, Ser. No. 259,844 4 Claims. (Cl. 313-222) This invention relates generally to electric incandescent lamps, and more particularly to incandescent lamps of the so called iodine cycle type comprising an elongated tubular envelope containing an axially extending tungsten filament and a filling if inert gas together with iodine vapor which functions as a regenerative getter to return to the filament tungsten vapor evolved therefrom during operation of the lamp to thereby prevent deposition of the tungsten vapor on the envelope wall as a dark coating. Such lamps are more fully disclosed and claimed in Patent 2,883,571, Fridrich and Wiley, which is assigned to the same assignee as the present invention.

Lamps of the aforesaid type have come into use with eminently successful results. However there is need for improvement in respect to operation of such lamps in a vertical position. When lamps of larger diameter, e.g., approximately 20 mm. internal diameter, are operated vertically the iodine vapor is maintained effective throughout the envelope by virtue of violent convention currents, However, when lamps having envelopes of desirably smaller diameter and a length greater than about three times the diameter, are operated in positions other than the horizontal, there takes place a thermal diffusion separation of iodine vapor from the inert gas. The iodine vapor becomes concentrated in the lower portion of the envelope with the result that the upper end of the envelope becomes coated with a dark deposit of tungsten vapor due to a deficiency of iodine.

Accordingly, it is an object of this invention to provide tubular iodine cycle lamps which will operate successfully in a vertical position as well as horizontally.

In accordance with one aspect of the invention, successful vertical operation of such lamps is achieved by employing an inert gas filling at a pressure above a minimum critical pressure which prevents significant separation of the iodine vapor from the gas during operation of the lamp and also prevents early formation of a dark wall deposit of vaporized tungsten.

For a further understanding of the invention attention is directed to the following detailed description and to the drawing which is a vertical elevation of a lamp embodying the invention.

Referring to the drawing, the lamp illustrated therein comprises a tubular envelope 1, preferably of quartz, having therein an axially extending filament 2 of helically coiled tungsten wire connected by straight end or leg portions 3 to extremely thin foliated seal portions 4 of molybdenum lead wires 5 hermetically sealed in pinch seal portions 6 at respective ends of the envelope. The filament 2 is supported at spaced intervals by support members 7 such as spirals of tungsten wire which are attached to the filament and support it from the inner envelope walls. The envelope 1 also contains a filling of inert gas and a quantity of iodine vapor introduced therein through an exhaust tube, the tipped ofif residue of which is shown at 8.

We have found that in the vertical operation of lamps having tubular envelopes of internal diameters within a range greater than 4 mm. and less than about 20 mm., separation of the iodine from the inert gas is significantly prevented and early bulb blackening is avoided by employing a critical minimum cold pressure (i.e., at ordinary room temperature of about 75 F.) of about 1500 3,240,975 Patented Mar. 15, 1966 mm. Hg in the case of xenon, 2500 mm. Hg in the case of krypton, and 3500 mm. Hg in the case of argon, when the filament has an operating true temperature of about 3100 K. The said minimum critical pressure varies with varying filament temperature; for example, for a filament true temperature of about 2950 K. the minimum pressures are decreased about 200 mm. Hg. The values of critical pressures were determined by tests of many lamps containing the different gases at difierent pressures and involving operation of the lamps and visual observation of the iodine separation immediately after turning off the lamps, as well as continued operation of the lamps and observation of early onset of blackening of the upper end of the envelopes, or operation to the end of life by normal filament burnout without bulb wall blackening.

For operation at the elevated pressures involved herein, it is preferred that the iodine content be at least about .02 micromole per cc. of envelope volume, for example about /2 to 1 micromole per cc. Also, as usual in the case of iodine cycle lamps, in order for the iodine cycle to func tion properly the filament loading must be such as to maintain the envelope walls at a temperature in excess of 250 0, usually about 600 to 700 C.

By way of specific example many of the lamps tested were of a 500 watt, T3, 120-volt variety with two different filament lengths for operation at respective nominal efliciencies of 21 lumens per watt and 26 lumens per watt and therefore designated hereinafter as 21 LPW and "26 LPW. The 21 LPW, 500 watt, T3, 120-volt lamps had envelopes of 8 mm. internal diameter, 10 mm. external diameter and about to 82 mm. internal length between the seals 4-4, the volume being about 4 cc. The filament 2 consisted of 278 coil turns of tungsten wire of 7.14 mils diameter and 44.3 mils outside diameter of the coil; the coil length was 71 mm. plus 8 mm. legs 3. The filament true temperature during operation was about 2950 K. The iodine content was 2.5 micromoles. The 26 LPW, 500 watt, T3, -volt lamp was the same except for an effective filament coil length of about 60 mm., operating at a true temperature of about 3115 K., and an internal envelope length of 69 to 71 mm. and volume of about 3 to 3.5 cc.

Tests were made of a number of lamps of the 26 LPW, 500 watt, T3, 120-volt type containing fillings of argon, krypton and xenon at pressures ranging from 1000 to 5500 mm. Hg and operated in a vertical position. It was found that lamps filled with argon below 3500 mm. Hg cold pressure, with krypton below 2500 mm. Hg pressure and with xenon below 1500 mm. Hg pressure were characterized by separation of the iodine and the onset of early blackening, for example in about 20 to 200 hours, whereas those containing higher pressures of the respective gases operated without wall deposits to burnout at lives ranging from about 700 to over 2000 hours depending upon pressure and type of gas. For the 21 LPW, 500 watt, T3, 120-volt lamp the said pressures are reduced by about 200 mm. Hg. In other words the critical pressure limit for vertical burning diminishes at lower filament temperatures, or more properly at lower temperature gradient between the filament and the envelope wall. It may be noted that the gas pressure during operation of the lamp is about 4 to 5 times the cold fill pressure.

Lamps of longer length have also been operated successfully in vertical positions when filled with gas above the aforesaid critical pressures. For example, 1500 watt, 2'70-volt lamps having a filament coil similar to that in the 500 watt lamp but 206 mm. long, an envelope of 8 mm. inside diameter and containing 7.5 micromoles of iodine and xenon at pressures of 2100 and 4000mm. Hg respectively burned in excess of 2500 hours and 2800 hours respectively with no envelope wall deposits.

Whereas lamps with inside envelope diameters as large as 20 mm. may be operated vertically at lower pressures than the aforesaid critical pressures because of the violent convection currents therein, lamps with envelopes as small as 4 mm. inside diameter showed separation of the iodine even at pressures as high as 2600 mm. Hg of xenon gas. Lamps having envelopes of 5 mm. inside diameter were operated vertically with no sign of thermal diffusion separation when filled at pressures above the critical pressures.

In connection with tests of lamps filled to cold pressures as high as 15,000 mm. Hg, it has been demonstrated that the life of these tubular iodine cycle lamps increases rapidly with increase in the gas pressure up to a maximum beyond which life appears to remain constant. This transition pressure is a function especially of the filament temperature and the inside diameter of the envelope. For the aforesaid 21 and 26 LPW, 500 watt lamps the values are approximately 4000 and 5000 mm. Hg respectively. For example, for the 21 LPW, T3, 500 watt lamp, a life of about 6000 hours may be attained with 3500 mm. Hg of argon. Also, forced Voltage operation of the 21 LPW lamp with high pressure (7100 mm. Hg of xenon) permits operation at voltages as high as 188 volts at an initial efiiciency of 40 lumens per watt for an average life of 180 hours. This corresponds to a filament temperature of 3500 K. (true) which is only 155 K. below the melting point of tungsten. For the higher pressures, say above about 5000 mm. Hg, it is desirable that the envelope be made of heavier walled tubing, such as 2 mm. thick.

It may be added that no apparent performance difierence has been observed between vertical or horizontal operations beyond the minimum critical pressures established for vertical operation. It also appears that an increase in iodine concentration to the higher amount of about /2 to 1 micromole per cc. of envelope volume, or more, is required for forced voltage operation where both higher filament temperatures and gas pressure prevail. It may further be noted that increasing the gas pressure to about 1000 to 1400 mm. Hg virtually eliminates envelope explosions due to arcing at end of life which tended to occur at lower gas pressure such as about 600 mm.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An iodine cycle electric incandescent lamp comprising a tubular envelope having an inside diameter greater than 4 mm. and less than about 20 mm. and a length exceeding three times the diameter, a coiled tungsten wire filament extending axially substantially the full length of said envelope, current supply conductors connected to respective ends of said filament and sealed through said envelope, a filling in said envelope of a gas selected from the group consisting of argon, krypton and xenon, and a quantity of iodine in said envelope functioning as a regenerative getter returning to said filament tungsten vapor evolved therefrom during operation of the lamp, said gas having a minimum pressure at ordinary room temperature of about 1300 mm. Hg for Xenon, 2300 mm. Hg for krypton and 3300 mm. Hg for argon and sufiiicent to prevent significant separation of the iodine vapor from said gas during operation of the lamp in a vertical position with a filament temperature of about 2950 K., the aforesaid minimum gas pressures being increased at the rate of about 200 mm. Hg for each increase in filament temperature of K.

2. A lamp as set forth in claim 1 wherein the envelope inside diameter is approximately 8 mm. and the iodine quantity is in the approximate range of .02 to 1 micromole per cc. of envelope volume.

3. A lamp as set forth in claim 2 wherein the filament has an operating temperature of about 3100 K. and the minimum gas pressure is about 1500 mm. for xenon, 2500 mm. for krypton and 3500 mm. for argon.

4. A lamp as set forth in claim 2 wherein the filament has an operating temperature of about 2950 K. and the minimum gas pressure is about 1300 mm. for xenon, 2300 mm. for krypton and 3300 mm. for argon.

References Cited by the Examiner UNITED STATES PATENTS 2,883,571 4/1959 Fridrich et al 3l3-222 X GEORGE N. WESTBY, Primary Examiner. 

1. AN IODINE CYCLE ELECTRIC INCANDESCENT LAMP COMPRISING A TUBULAR ENVELOPE HAVING AN INSIDE DIAMETER GREATER THAN 4 MM. AND LESS THAN ABOUT 20 MM. AND A LENGTH EXCEEDING THREE TIMES THE DIAMETER, A COILED TUNGSTEN WIRE FILAMENT EXTENDING AXIALLY SUBSTANTIALLY THE FULL LENGTH OF SAID ENVELOPE, CURRENT SUPPLY CONDUCTORS CONNECTED TO RESPECTIVE ENDS OF SAID FILAMENT AND SEALED THROUGH SAID ENVELOPE, A FILLING IN SAID ENVELOPE OF A GAS SELECTED FROM THE GROUP CONSISTING OF ARGON, KRYPTON AND XENON, AND A QUANTITY OF IODINE IN SAID ENVELOPE FUNCTIONING AS A REGENERATIVE GETTER RETURNING TO SAID FILAMENT TUNGSTEN 